1. Field of the Invention
The present invention relates to a near-field light generator including a waveguide and a plasmon generator, and to a thermally-assisted magnetic recording head including the near-field light generator.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and magnetic recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the magnetic recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the magnetic recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the aforementioned problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a magnetic recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the magnetic recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the magnetic recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating the near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near a medium facing surface of the slider.
The plasmon generator that generates near-field light by direct irradiation with light is known to exhibit very low efficiency of transformation of the applied light into near-field light. The energy of the light applied to the plasmon generator is mostly reflected off the surface of the plasmon generator, or transformed into thermal energy and absorbed by the plasmon generator. The plasmon generator is small in volume since the size of the plasmon generator is set to be smaller than or equal to the wavelength of the light. The plasmon generator therefore shows a significant increase in temperature when it absorbs the thermal energy.
Such an increase in temperature causes the plasmon generator to expand in volume and protrude from the medium facing surface. This increases the distance from the read head unit and the write head unit to the surface of the magnetic recording medium, thereby possibly causing degradation of the characteristics of the thermally-assisted magnetic recording head. Furthermore, an increase in temperature of the plasmon generator can degrade the magnetic property of a magnetic pole for producing a write magnetic field in the write head unit, and can thereby degrade the characteristics of the write head unit. These problems caused by an increase in temperature of the plasmon generator become prominent when the thermally-assisted magnetic recording head is used continuously for many hours.
To cope with this, there has been proposed such a technique that the surface of the core of the waveguide and the surface of the plasmon generator are arranged to face each other with a gap therebetween, so that evanescent light that occurs from the surface of the core based on the light propagating through the core is used to excite surface plasmons on the plasmon generator to generate near-field light based on the surface plasmons. The technique is disclosed in, for example, U.S. Pat. No. 7,330,404.
The aforementioned technique allows the light propagating through the core to be transformed into near-field light with high efficiency, and also allows the plasmon generator to be prevented from excessively increasing in temperature because the plasmon generator is not directly irradiated with the light propagating through the core.
Even with the aforementioned technique, however, an increase in temperature of the plasmon generator still occurs because part of the energy of the light propagating through the core is transformed into heat in the plasmon generator.
To increase the intensity of near-field light generated from the plasmon generator, it is required to increase the intensity of surface plasmons excited on the plasmon generator. As the intensity of surface plasmons excited on the plasmon generator increases, the amount of energy transformed into heat in the plasmon generator increases, and the problems resulting from an increase in temperature of the plasmon generator thus become more significant.
Conventionally, it has therefore been difficult to increase the intensity of near-field light generated from the plasmon generator while preventing an increase in temperature of the plasmon generator.